1. Field of the Invention
The present invention relates to a method and an apparatus for identifying a base station in a wireless communication system. More particularly, the present invention relates to a method and an apparatus for allowing User Equipment (UE) to identify a macro base station and a femto base station using a Neighbor Cell List (NCL) and a Physical Cell IDentifier (PCID) of each base station.
2. Description of the Related Art
In a cellular wireless communication system, a channel status is deteriorated due to a geographical factor inside a cell, a distance between a User Equipment (UE) and a base station, or movement of the UE. Therefore, communication between the UE and the base station is not promptly performed. More particularly, when the UE is located inside a closed building, such as an office or a house, a channel between a base station and the UE is deteriorated because a shadow region is formed. The UE located in the shadow region cannot promptly perform communication with the base station.
Recently, a femto cell concept is proposed in order to provide a high level data service to more users while solving a service limitation of an indoor shadow region. As illustrated in FIG. 1, the femto cell is a small cell area formed by a femto base station which accesses a mobile communication core network via a broadband network installed inside an indoor space. Since the femto cell has a very small cell area compared to a macro cell, a plurality of femto cells may be installed inside one macro cell area. Also, a subscriber may pay an installation cost of the femto base station, and install and remove the femto base station themselves. Therefore, only a registered subscriber may use the femto base station.
When a signal is received from a base station, the UE needs to identify whether the base station is a macro base station or a femto base station. Also, if the base station is a femto base station, the UE needs to identify whether the femto base station is a femto base station which may be used by the UE. Such identification of a base station may be achieved through an identifier included in a system information message, but an identification method using the system information message requires a long processing time and a resource for the processing.
A macro base station assigns one Physical Cell IDentifier (PCID) to a femto base station located in a service area of the macro base station. At this point, the number of PCIDs which the macro base station may assign to the femto base stations is limited. Therefore, when a number of femto base stations greater than the number of PCIDs which may be assigned to the femto base stations exist in the service area of the macro base station, the macro base station assigns a repeated PCID to the femto base stations. In this case, a problem occurs in which the UE cannot identify femto base stations having the same PCID.
Therefore, various conventional techniques for performing the above-described identification of a base station in a physical layer are performed. Examples of the conventional techniques include a method for using an identifier which classifies PCIDs into PCIDs for femto base stations and PCIDs for macro base stations, a method for discriminating a range of a PCID of a femto base station from a range of a PCID of a macro base station, a method for using frequencies differently for a femto base station and a macro base station, and a method for using an identifier included in an NCL.
However, the method for using an identifier which classifies PCIDs into PCIDs for femto base stations and PCIDs for macro base stations, and the method for using an identifier included in an NCL necessarily cause modification of a standard. Therefore, these methods cannot support existing UEs. Also, the method for discriminating the ranges of PCIDs is limited when a ratio of a femto base station and a macro base station is different for each business and each region. Therefore, PCIDs should be operated differently. Also, the method for using frequencies differently cannot support a business depending on a resource of the business.
Therefore, a need exists for a method and an apparatus for identifying a macro base station and a femto base station in a wireless communication system.